Catheters are tubular medical devices which, when inserted into canals, vessels, passageways and the like of a human or animal, permit injection or withdrawal of fluids. In several applications, such as parenteral nutrition, cancer chemotherapy, and frequent antibiotic therapy, the correct placement of the tip of the catheter is essential. As a result, the prior art provides for methods and devices to accurately determine the location of the tip of a catheter within a patient's body. One such method and device for detecting the tip of a catheter is disclosed in U.S. Pat. No. 4,905,698 to Strohl, Jr. et al., the disclosure of which is incorporated herein by reference.
In general, the Strohl method and device utilizes a source which generates an alternating magnetic field, and a detector positioned proximate the distal end of the catheter. The detector generates a voltage in response to the proximity of the field generated by the source. The phase of the voltage in the detector shifts as the source passes over it. By referencing anatomical landmarks at the time the phase shift occurs, the caregiver can determine the exact location of the detector, and thus the location of the tip of the catheter.
The detector consists of a magnetic core and a pair of leads that are wrapped around the core and fed through the lumen of the catheter to a power source. The magnetic core and leads are housed within a protective sheath to form a detector assembly. When an electric current passes through the leads, the position of the distal end of the catheter may be located. Once the tip of the catheter is properly positioned, the detector assembly may be removed.
As the detector assembly is removed from the catheter, it is subject to various forces. There is, of course, the pulling force applied by the caregiver as he or she pulls on the sheath to remove the detector assembly from the catheter. In particular, the sheath is subject to frictional forces exerted by the inner walls of the catheter as the detector assembly is withdrawn therefrom. As the caregiver pulls on the detector assembly, the sheath elongates while the leads of the detector tighten. Depending on the amount of force used by the caregiver, the leads of the detector can snap, thereby making the detector inoperable. In some cases, such as when the catheter is placed in tortious configurations within the patient's body, the caregiver must twist and turn the sheath. As a result, the force necessary to remove the detector assembly under such hard extractions may cause damage not only to the detector, but also to the sheath. The sheath is also subject to forces resulting from the physical compression associated with the placement of the catheter into a patient's body. Consequently, the sheath material and its structural configuration must possess frictional, tensile, and flexibility properties to withstand such forces and thus, prevent it and the detector from being damaged when removed from the catheter. As a result, the selection of the sheath material and its structural configuration are critical.
One of the commonly used materials for sheaths in the past was polyethylene. While polyethylene is compatible with the recently emerging polyurethane catheters, it is not compatible with conventional silicone catheters. When a polyethylene sheath is used with a silicone catheter, the polyethylene tends to bind on the silicone. This binding effect makes it extremely difficult to remove the detector assembly from the catheter without causing damage thereto. Silicone catheters, however, are desirable since they possess elastic properties that are compatible with the functions required to be performed by the catheter within the body.
Polyethylene has several other shortcomings. First, polyethylene does not have the tensile strength necessary to withstand the forces required to pull the detector assembly out of the catheter. Second, a polyethylene sheath often cannot withstand the forces resulting from the physical interactions associated with the placement of the catheter into a patient's body. Consequently, polyethylene has not proven very effective for sheaths, especially when used with silicone catheters.
A disadvantage with existing sheaths regardless of their material makeup is their generally flat outer surface configuration. While such a configuration is simple and thus inexpensive to manufacture, it inhibits the removal of the detector assembly by increasing the amount of contact between the outer surface of the sheath and the inner walls of the catheter. As a result, more force must be applied to the detector assembly in order to remove it from the catheter. The risk of sheath and detector breakage is thus further increased.
The above-mentioned shortcomings of existing sheaths also present financial concerns. Hospitals and like facilities must keep excess inventory of detector assemblies in order to account for the high potential for damaged detectors and/or sheaths. Moreover, when a detector assembly is damaged, the catheter must also be removed and discarded regardless of whether or not it has, in fact, been damaged. As a result, an excess inventory of catheters must also be maintained. A typical catheter and detector assembly can cost about $150.00 (U.S. Dollars). In the case of more sophisticated catheters, such as those having implantable reservoirs, the costs can often exceed about $500.00 (U.S. Dollars). In an average-sized medical facility, even a low damage rate can be quite costly. In light of the heightened awareness to reduce healthcare costs, such waste is unacceptable.
The disadvantages associated with existing sheaths, however, are not solely economical. The insertion and removal of a catheter can be quite painful and discomforting to the patient. More importantly, breakage of the sheath can be life threatening. For example, broken pieces of the detector may travel down the catheter and migrate into the patient's vascular stream. It is possible that the caregiver may need to perform surgery to remove the broken pieces. In terms of providing a high standard of patient care, the minimization of insertions and removals of the catheter and of surgery is critical. This is especially true in light of the increased competition among doctors and medical facilities.
Accordingly, there is a need for a catheter apparatus that allows for safe and easy removal of a detector from the lumen of a catheter.